The present invention relates to an image forming apparatus that forms an image on a medium according to image data.
In an image forming apparatus such as a photocopier, facsimile, printer, and multi-functional peripheral provided with functions of a plurality of these devices, a latent image is written onto the image carrier (such as a photoreceptor) by the LD (Laser Diode) and others in conformity to the image data. This is developed by toner, and the toner image having been obtained is transferred onto a medium directly or through an intermediate transfer body, whereby an image is formed. The medium is mounted on a sheet feed tray inside or outside the image forming apparatus. This medium is conveyed and supplied for the image formation. The front end of the medium is detected by a front end detecting sensor or the like, and the image forming position on the medium is adjusted in conformity to the timing of the detection.
Incidentally, when the medium is conveyed, position shift may occur to the medium in the direction perpendicular to the direction of conveyance. If image formation is performed under this condition, an image of poor positioning accuracy will be produced. To avoid this, the end position in the main scanning direction of the medium being conveyed is detected by an uneven-distribution sensor or the like to find out the amount of misalignment. The position for image formation is corrected in conformity to this misalignment of paper.
In this case, the main scanning direction of the medium means a direction on the medium, which is equivalent to the main scanning direction of forming a latent image of an image, at the moment of transferring the image to the medium.
To implement this method, the amount of misalignment of paper must be detected before starting image Formation. However, the tandem color image forming apparatus or the like requires a longer time for image formation than the black-and-white image forming apparatus. With this time taken into account, the end position of paper in the main scanning direction must be detected somewhat far upstream of the image forming section. Further, in the black-and-white image forming apparatus as well, the end position of paper is detected at some distance upstream of the image forming section, with consideration given to the time required for image formation. However, as detection is performed at a greater distance from the image forming section, there will be a greater possibility of misalignment caused by subsequent conveyance. This reduces the position accuracy of the image formation.
To solve this problem, proposals have been made to install a device for moving paper in the main scanning direction, and to move the paper in response to the amount of misalignment of paper in the main scanning direction, whereby the image forming position is adjusted (Japanese Unexamined Patent Application Publication No. 2002-338088, Japanese Unexamined Patent Application Publication No. 01-192649, Japanese Unexamined Patent Application Publication No. 04-277150, Japanese Unexamined Patent Application Publication No. 2003-263090, and Japanese Unexamined Patent Application Publication No. 64-8159). A reference plate called a lateral registration plate is generally used in the image forming apparatus disclosed in the Japanese Unexamined Patent Application Publication No. 2002-338088, Japanese Unexamined Patent Application Publication No. 01-192649, Japanese Unexamined Patent Application Publication No. 04-277150, and Japanese Unexamined Patent Application Publication No. 2003-263090. This reference plate is moved in the lateral direction, whereby the paper position is adjusted. In the image forming apparatus disclosed in the Japanese Unexamined Patent Application Publication No. 64-8159, paper is moved in the lateral direction by the lateral movement of the roller which nips paper, whereby the paper position is adjusted.
However, the following problem is found in the image forming apparatus disclosed in the Japanese Unexamined Patent Application Publication No. 2002-338088, Japanese Unexamined Patent Application Publication No. 01-192649, Japanese Unexamined Patent Application Publication No. 04-277150, and Japanese Unexamined Patent Application Publication No. 2003-263090. Namely, when the reference plate is moved in the lateral direction, the plate must be returned to the standard position for each page in order to avoid interference with the succeeding paper subsequent to position adjustment. This arrangement fails to meet the requirement of high-speed paper conveyance, and if paper is conveyed in response to the movement of the reference plate, productivity will be reduced.
In the meantime, in the image forming apparatus disclosed in the Japanese Unexamined Patent Application Publication No. 64-8159, paper position is adjusted by the lateral movement of the roller. This invention meets the requirement for high-speed paper conveyance, without having to return the roller. However, there is a limit to the roller moving range. Beyond this range, paper position adjustment is accompanied by difficulties. This makes it necessary to control the roller position so that the limit of roller movement will not be reached.
One of the proposals refers to the method, wherein a movable limit detector is installed, and the page-by-page control is provided in such a way as to move the roller by the amount of paper misalignment from a predetermined position. When the movable limit has been reached, the operation is suspended and the roller is returned to the standard position. Another proposal refers to the method wherein, subsequent to correction of the misalignment of paper for each page, the roller is returned to the standard position between sheets of paper.
However, any of these methods is accompanies by the problem of reducing the productivity. Moreover, very complicated high-speed operation must be performed in order to minimize the reduction in productivity in the method of returning the roller to the standard position for each page.
To be more specific, of the image forming apparatuses of the embodiments of the present invention, the image forming apparatus of the first embodiment for forming an image on a medium according to image data includes:
a moving roller capable of axial movement in the main scanning direction for the purpose of ensuring that the aforementioned medium during conveyance is moved in the main scanning direction to perform position adjustment in preparation for the aforementioned image formation;
a medium end position detecting section for detecting the end position of the aforementioned medium in the main scanning direction; and
a control section for calculating the amount of misalignment of the medium in the main scanning direction from the end position detected by the medium end position detecting section;
wherein the control section obtains the correction amount of the image forming position according to the amount of misalignment of the medium having been calculated, and provides control in such a way that the medium coming later than the aforementioned medium by a predetermined number of pages is moved by the aforementioned moving roller by the difference between the correction amount of the image forming position and the amount of misalignment of the medium coming later by a predetermined number of pages, and the image forming position is corrected according to the correction amount.
The image forming apparatus of the second embodiment for forming an image on a medium according to image data includes:
a moving roller capable of axial movement in the main scanning direction for the purpose of ensuring that the aforementioned medium during conveyance is moved in the main scanning direction to perform position adjustment in preparation for the aforementioned image formation;
a medium end position detecting section for detecting the end position of the aforementioned medium in the main scanning direction; and
a control section for calculating the amount of misalignment of the medium in the main scanning direction from the end position detected by the medium end position detecting section;
wherein the control section obtains the correction amount of the image forming position according to the amount of misalignment of the medium having been calculated, and information on the moving position of the roller, and provides control in such a way that the medium coming later than the aforementioned medium by a predetermined number of pages is moved by the aforementioned moving roller by the difference between the correction amount of the image forming position and the amount of misalignment of the medium coming later by a predetermined number of pages, and the image forming position is corrected according to the correction amount.
The image forming apparatus of the third embodiment for forming an image on a medium according to image data includes:
a moving roller capable of axial movement in the main scanning direction for the purpose of ensuring that the aforementioned medium during conveyance is moved in the main scanning direction to perform position adjustment in preparation for the aforementioned image formation;
a medium end position detecting section for detecting the end position of the aforementioned medium in the main scanning direction; and
a control section for calculating the amount of misalignment of the medium in the main scanning direction from the end position detected by the medium end position detecting section;
wherein the control section corrects the image forming position on the medium according to the amount of misalignment of the medium having been calculated, and moves the medium by using the aforementioned moving roller by the difference between correction amount of the image forming position and the amount of misalignment of the medium.
The image forming apparatus of the fourth embodiment for forming an image on a medium according to image data includes:
a moving roller capable of axial movement in the main scanning direction for the purpose of ensuring that the aforementioned medium during conveyance is moved in the main scanning direction to perform position adjustment in preparation for the aforementioned image formation;
a medium end position detecting section for detecting the end position of the aforementioned medium in the main scanning direction; and
a control section for calculating the amount of misalignment of the medium in the main scanning direction from the end position detected by the medium end position detecting section;
wherein the control section corrects the image forming position on the medium according to the amount of misalignment of the medium having been calculated and the information on the moving position of the roller, and moves the medium by using the aforementioned moving roller by the difference between the correction amount of the image forming position and the amount of misalignment of the medium.